@gulthaw @xssfox
IIUC it depends on how you define a postcode. Loosely, residential postcodes cover one side of a street and you then need either the name or number of the building to specify.
There are also organisational postcodes, some of which are not geographical (e.g. a site I worked on, which had quasi-governmental status, had a postcode which applied to the site only, but was out of sequence for the area - reading it directly you'd assume it was in the county town, not 10 miles away).